1. Field of the Invention
The present invention relates to a high-permittivity rubber compounds and power cable members.
2. Description of Relevant Art
The XLPE (crosslinked polyethylene) cable, applicable as a power cable for general purposes, has at its connected or terminated portion various insulated or insulating parts (e.g., inner electrode layer, semi-conductive outer electrode layer, stress cone with a rise, and boundaries between cable core and connection elements), where the insulation is effected with materials installed therefor (e.g., fitted rubber mold, wound rubber tape, or filled epoxy resin) sometimes by on-site work, which may be manual.
Forming insulation layers by manual work tends to accompany on the boundary certain singular points very large or disconnected of curvature, such as a small projection, foreign material, or void, causing the electric field in insulation layer to be steep of gradient about such singular points, needing careful attention and qualified skill in order to achieve a secure prevention of dielectric breakdown, resulting in increase in cost and time for installation.
To this point, using an insulator high of permittivity allows for the electric field to moderate in gradient. It was examined in the past to use as an insulator a rubber compound having a relative permittivity increased by filling a conductive filler such as carbon black, or a rubber compound inherently high of permittivity, such as an acrylic rubber or fluororubber.
The filling of conductive filler formed a chain of conductive particles. The use of a rubber compound inherently high of permittivity, of which polymer has a prominent polarity, brought a fall in dielectric loss tangent, as well as in dielectric breakdown voltage or insulation resistance. In either case, the insulation performance was significantly degraded, as a problem.
It was tried to provide a rubber compound filled with a filler relatively high of relative permittivity, such as barium titanate or titanium oxide. However, as the amount of filler was simply increased, the rubber compound had an increased permittivity, with significant degradation of insulation performance, as a problem.